JP2002260632A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-capacity secondary battery of a non-aqueous electrolyte type superior in safety and moreover having superior high-temperature cycle characteristic. SOLUTION: This secondary battery uses a mixture of lithium manganate with lithium nickelate as a positive electrode active material, and contains at least one kind of element selected from Bi, Pb, Sb and Sn in the positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a secondary battery,
More specifically, it is suitably used for a secondary battery using a non-aqueous electrolyte such as a lithium secondary battery or a lithium ion secondary battery, and can have a high capacity, and has safety and operating characteristics, particularly high-temperature cycle characteristics. It relates to an excellent secondary battery.

[0002]

2. Description of the Related Art Conventionally, in a non-aqueous electrolyte secondary battery using lithium metal or a lithium compound as a negative electrode, when lithium cobaltate, lithium nickelate, and spinel type lithium manganate are used as a positive electrode active material, the voltage exceeds 4 V. Research has been extensively conducted because an electromotive force can be obtained. Above all, lithium cobaltate is widely used as a positive electrode active material of a lithium ion secondary battery at present because of its excellent battery characteristics and easy synthesis.

[0003] However, since cobalt has a small recoverable reserve and is expensive, lithium nickelate is promising as a substitute for cobalt. This lithium nickelate has a layered rock salt structure (α-NaFe) like lithium cobaltate.
O ₂ structure) has, for having a potential of about 4V to lithium electrode, the capacity is very high capacity to about 200 mAh / g of lithium cobaltate in the range of 4.2V or less based on lithium ,Attention has been paid.

By the way, in this layered rock salt structure, an oxygen phase having a large electronegativity becomes adjacent due to elimination of lithium at the time of charging, and when the electrostatic repulsion between the oxygen layers exceeds the chemical bonding force, the CdCl ₂ structure is formed. An irreversible structural change to Such structural instability during charging also correlates with the chemical instability of Ni ⁴⁺ generated by charging, and affects the temperature at which oxygen desorption from the crystal lattice starts. It has been reported that lithium nickelate in a charged state has a lower oxygen desorption initiation temperature than lithium cobaltate (see Solid State Ionics, 69, No. 3/4, 265 (1994)). ).

Therefore, a battery system using lithium nickel oxide alone as a positive electrode active material is not practically used because sufficient stability cannot be ensured due to thermal instability during charging, although high capacity can be expected. Is difficult. Also,
It has already been reported that in this battery system, the reaction for decomposing the electrolytic solution easily proceeds, and the cycle characteristics, particularly the cycle characteristics at high temperatures, are not sufficient (J. Electrochem.
Soc. 147 p.1322-1331 (2000)).

On the other hand, spinel-type lithium manganate has a crystal structure belonging to the space group Fd3m, and its lamination pattern in the (111) crystal axis direction is different from lithium cobaltate or lithium nickelate, and is different from lithium cobaltate or lithium nickelate. Is known not to exist. For this reason, even if all the lithium is extracted, the manganese ions become pillars, so that the oxygen layer does not directly adjoin. Therefore, it is possible to extract lithium ions while maintaining the cubic basic skeleton. Also, the oxygen desorption start temperature during charging is
The temperature is higher than that of lithium nickelate or lithium cobaltate having a layered rock salt structure, which also indicates that spinel-type lithium manganate is a highly safe cathode material.

However, the battery system using the spinel type lithium manganate has a problem that the charge and discharge capacity is smaller than that using the lithium cobaltate or lithium nickelate. Further, Mn is contained in the electrolyte at a high temperature.
It has been pointed out that the high-temperature cycle characteristics are insufficient due to elution. Therefore, a nonaqueous electrolyte secondary battery having a high capacity and improved safety has been proposed by using a spinel-type mixture of lithium manganate and lithium nickelate as a positive electrode active material (Japanese Patent Application Laid-Open No. 2000-2000). 770
No. 72). This non-aqueous electrolyte secondary battery has a higher capacity than lithium cobalt oxide, and ensures safety.

[0008]

The above-mentioned non-aqueous electrolyte secondary battery is characterized by being superior to conventional secondary batteries in terms of high capacity and safety. In this case, the cycle characteristics at high temperatures are not sufficient, and further improvement is required. Furthermore, in a secondary battery using spinel-type lithium manganate, a chalcogen compound containing at least one element selected from the group consisting of Ge, Sn, Pb, In, Sb, Bi, and Zn in a positive electrode. A technique of improving the battery characteristics at high temperatures by adding the same has already been disclosed (Japanese Patent Laid-Open No.
This secondary battery uses a spinel-type lithium manganate alone as a positive electrode active material, and uses a mixture of spinel-type lithium manganate and lithium nickelate as a positive electrode active material. The point of use is not considered at all.

In a secondary battery using lithium cobaltate or lithium nickelate, B, Bi, Mo,
A technique in which the internal resistance of a battery is reduced by adding at least one element selected from P, Cr, V, and W has already been disclosed (see Japanese Patent Application Laid-Open No. 2000-113884). For the secondary battery, there is no description about battery characteristics at high temperatures. Thus, by using a mixture of lithium nickelate and spinel-type lithium manganate as the positive electrode active material, it is possible to obtain a secondary battery with higher capacity and higher safety than that using lithium cobaltate. However, even in this secondary battery, since the cycle characteristics at high temperatures are not sufficient, it is desired to improve the high-temperature cycle characteristics.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having high capacity, excellent safety, and excellent high-temperature cycle characteristics. Aim.

[0011]

Means for Solving the Problems The present inventor has made intensive studies to achieve the above object, and as a result, completed the present invention. That is, the secondary battery according to claim 1 of the present invention is:
In a secondary battery using a mixture of lithium manganate and lithium nickelate as a positive electrode active material, the positive electrode includes at least one element selected from Bi, Pb, Sb, and Sn.

The secondary battery according to a second aspect of the present invention is the secondary battery according to the first aspect, wherein the lithium manganate is Li _x Mn ₂ O ₄ (where 1.02 ≦ x ≦ 1.25).
Wherein the lithium nickelate is LiNi _1-x M _x O ₂
(Where M is at least one element selected from Co, Mn, Fe, Al and Sr, 0 <x ≦ 0.5).

The secondary battery according to claim 3 of the present invention is the secondary battery according to claim 1 or 2, wherein the weight ratio of the lithium manganate and the lithium nickelate is a:
100-a (where 40 <a ≦ 99).

A secondary battery according to a fourth aspect of the present invention is the secondary battery according to the first, second or third aspect, wherein the element is added in a state of carbonate, hydroxide or oxide. It is characterized by the following.

According to a second aspect of the present invention, in the secondary battery according to the fourth aspect, the carbonate, hydroxide or oxide is 0.5% by weight with respect to the mixture. It is characterized in that it is contained in an amount of not less than 10%.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the secondary battery of the present invention
Will be described by taking a non-aqueous electrolyte secondary battery as an example. Real truth
The non-aqueous electrolyte secondary battery of the embodiment is Li_xMn_TwoO_Four(T
However, a spinel type represented by 1.02 ≦ x ≦ 1.25)
Lithium manganate and LiNi_1-xM_xO _Two(However,
M is a kind selected from Co, Mn, Fe, Al and Sr
The nickel oxide represented by the above elements, 0 <x ≦ 0.5)
A secondary battery using a mixture of titanium as the positive electrode active material.
Selected from Bi, Pb, Sb, and Sn in the positive electrode.
At least one element is a carbonate, hydroxide or acid
Is added in the form of a compound.

In this non-aqueous electrolyte secondary battery, since a mixture of spinel-type lithium manganate and lithium nickelate is used as the positive electrode active material, the cycle deterioration at a high temperature is independently caused by the positive electrode active material. Behavior is different from that of For this reason, it is considered that such a cycle deterioration cause is a result of the interaction between the active materials. For example, a product generated by the decomposition of the electrolytic solution at the electrode interface of lithium nickelate adversely affects lithium manganate.

Therefore, Bi, P
When at least one element selected from b, Sb and Sn is added in the form of carbonate, hydroxide or oxide,
The effect of suppressing the decomposition of the electrolytic solution or the adverse effect of the product thereof on the other active material is produced.

In this nonaqueous electrolyte secondary battery, the manganese (Mn) raw material of lithium manganate used as a positive electrode active material includes electrolytic manganese dioxide (EMD), Mn
Various Mn oxides such as ₂ O ₃ , Mn ₃ O ₄ and chemically synthesized manganese dioxide (CMD), and manganese compounds such as manganese salts such as manganese carbonate and manganese oxalate can be used. As the lithium (Li) raw material, And lithium compounds such as lithium carbonate, Li oxide, lithium nitrate and lithium hydroxide.

In lithium nickelate, nickel compounds such as nickel hydroxide, nickel oxide and nickel nitrate can be used as nickel (Ni) raw materials, and lithium carbonate and lithium nitrate can be used as lithium (Li) raw materials. And lithium compounds such as lithium hydroxide. Some elements (Co, Mn, Fe, Al, S, S) are used for stabilization, high capacity, safety improvement, etc.
r) may be doped.

The lithium manganate or lithium nickelate mixed in the positive electrode preferably has a particle size of 30 μm or less in consideration of the filling property of the positive electrode and the prevention of deterioration of the electrolytic solution. In addition, those without adsorbed water or structured water,
Alternatively, those subjected to heat dehydration treatment are preferable.

Bi, Pb, Sb, added to the positive electrode
The carbonate, hydroxide or oxide containing at least one element of Sn may be added at the time of powder production or at the time of electrode production, or any of lithium manganate and lithium nickelate to be mixed. It may be added to only one of them. However, in consideration of workability, it is desirable to add them together with a conductivity-imparting agent, a binder, and an organic solvent during electrode fabrication. From the viewpoint of the effect of improving the cycle characteristics at 45 ° C., the addition of Bi is the most effective. Therefore, it is desirable to select Bi as the additional element.

Next, the non-aqueous electrolyte secondary battery of the present invention will be described in more detail. As the positive electrode active material, a mixture of the above-described lithium manganate and lithium nickelate is suitably used. On the other hand, as the negative electrode active material, lithium, lithium alloy, graphite capable of inserting and extracting lithium, or a carbon material such as amorphous carbon is preferably used. The separator is not particularly limited, but a woven fabric, a glass fiber, a porous synthetic resin film, or the like can be used. For example, a polypropylene or polyethylene porous film is suitable in terms of a thin film, large area, film strength and film resistance.

As the solvent of the non-aqueous electrolyte, those commonly used may be used, and for example, carbonates, chlorinated hydrocarbons, ethers, ketones, nitriles and the like are preferably used. Particularly preferably, at least one of ethylene carbonate (EC), propylene carbonate (PC), and γ-butyrolactone (GBL) is used as the high dielectric constant solvent, and diethyl carbonate (DEC) and dimethyl carbonate (DMC) are used as the low viscosity solvent. , Ethyl methyl carbonate (EMC), esters and the like, and a mixture thereof is suitably used.

As the supporting salt, LiClO_Four, LiI,
LiPF₆, LiAlCl_Four, LiBF_Four, CF_ThreeSO_ThreeL
At least one kind selected from i.
You. Electrolyte and supporting salt are used for battery environment and battery
It is sufficient to select and adjust as appropriate taking into account optimization etc.
Is, as a supporting salt, 0.8 to 1.5 M LiClO _Four,
LiBF_FourOr LiPF₆And EC + as a solvent
At least DEC, PC + DMC, PC + EMC
It is desirable to use one kind.

As the configuration of the nonaqueous electrolyte secondary battery, various shapes such as a rectangular shape, a paper type, a laminated type, a cylindrical type, and a coin type can be adopted. In addition, the components include a current collector, an insulating plate, and the like, but these are not particularly limited, and may be appropriately selected according to the above shape.

Hereinafter, the nonaqueous electrolyte secondary battery of the present embodiment will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 In order to synthesize spinel type lithium manganate, lithium carbonate (Li ₂ CO ₃ ) and electrolytic manganese dioxide (EMD) were used as starting materials, and these materials were used in a molar ratio of [Li] / [Mn]. ] = 1.05 / 2. Next, this mixed powder was fired at 800 ° C. in an atmosphere of oxygen flow.

Lithium nickelate is used as a nickel source.
Nickel nitrate, lithium hydroxide as the lithium source,
Each is used, and a Co compound such as carbonic acid is used as an additional element.
Use cobalt and mix them to achieve the desired composition ratio.
And then fired at 750 ° C. in an oxygen flow atmosphere
Was. Here, the composition after firing is LiNi_0.8Co_0.2O _Two
The molar ratio of the raw materials was adjusted so that

Next, lithium manganate, lithium nickelate, a conductivity-imparting agent, and bismuth hydroxide are dry-mixed and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) in which PVDF as a binder is dissolved. To make a slurry. Next, this slurry was applied on an aluminum metal foil having a thickness of 25 μm, and then NMP was evaporated to obtain a positive electrode sheet. Here, the solid content ratio in the positive electrode is expressed by weight% of lithium manganate: lithium nickelate: conductivity imparting agent: bismuth hydroxide: PVDF = 45:
35: 10: 3: 7 (% by weight).

On the other hand, the negative electrode sheet is made of carbon and PVD.
F was mixed so as to have a ratio of carbon: PVDF = 90: 10 (% by weight), and this mixture was dispersed in NMP, and applied to a copper foil having a dispersed thickness of μm to prepare the same. As the electrolyte, 1M LiPF ₆ was used as a supporting salt, and a mixed solution of ethylene carbonate (EC) + diethyl carbonate (DEC) = 50 + 50 (vol%) was used as a solvent. As the separator, a polyethylene porous membrane having a thickness of 25 μm was used.

Example 2 In order to synthesize spinel-type lithium manganate, lithium carbonate (L
i ₂ CO ₃ ), electrolytic manganese dioxide (EMD) and bismuth oxide (Bi ₂ O ₃ ), and these are used in a molar ratio of [Li].
/[Mn]/[Bi]=1.05/2/0.05. Next, the mixed powder was fired at 800 ° C. in an atmosphere of oxygen flow to obtain a Bi-added spinel-type lithium manganate. Further, lithium nickelate was produced in the same manner as in Example 1.

Next, Bi-added lithium manganate, lithium nickelate, and a conductivity-imparting agent are dry-mixed and uniformly dispersed in N-methyl-2-pyrrolidone (NMP) in which PVDF as a binder is dissolved. And Next, this slurry was applied on an aluminum metal foil having a thickness of 25 μm, and then NMP was evaporated to obtain a positive electrode sheet. Here, the solid content ratio in the positive electrode is
Bi-added lithium manganate: lithium nickelate: conductivity-imparting agent: PVDF = 45: 40: 10: 5 (% by weight). Other battery configurations were the same as in Example 1, and a cylindrical cell was prototyped.

Comparative Example 1 A spinel type lithium manganate alone was used as the positive electrode active material, and the solid content ratio was lithium manganate: conductivity imparting agent: PVDF = 80: 10: 1.
A trial production of a cylindrical cell was performed in the same manner as in Example 1 except that 0 (wt%) was used.

Comparative Example 2 Example 1 was repeated except that only lithium nickelate was used as the positive electrode active material and the solid content ratio was lithium nickelate: conductivity imparting agent: PVDF = 80: 10: 10 (% by weight). A prototype of a cylindrical cell was produced in the same manner as in Example 1.

Comparative Example 3 Bi-added spinel-type lithium manganate produced in the same manner as in Example 2 was used as the positive electrode active material, and the solid content ratio was Bi-added spinel-type lithium manganate: conductivity imparting agent: PVDF = 80: 10: 1
A trial production of a cylindrical cell was performed in the same manner as in Example 1 except that 0 (% by weight) was used.

Comparative Example 4 Only lithium nickelate was used as the positive electrode active material, and the solid content ratio was lithium nickelate: conductivity imparting agent: bismuth oxide: PVDF = 75: 1.
A cylindrical cell was prototyped in the same manner as in Example 1 except that the ratio was 0: 5: 10 (% by weight).

Comparative Example 5 A mixture of spinel-type lithium manganate and lithium nickelate was used as the positive electrode active material, and the solid content ratio was changed to spinel-type lithium manganate: lithium nickelate: conductivity imparting agent: PVDF = 45: 3.
A cylindrical cell was prototyped in the same manner as in Example 1 except that the ratio was 5:10:10 (% by weight).

"Characteristic evaluation" Examples 1 and 2 and Comparative Example 1
The charge / discharge cycle test at 45 ° C. was performed using the cylindrical cells prepared in the steps No. 5 to No. 5. The charging was performed up to 4.2 V at 0.5 A, and the discharging was performed up to 3.0 V at 1 A. Table 1 shows the charge / discharge capacity in the first cycle.

[Table 1]

FIG. 1 shows Examples 1 and 2 and Comparative Example 5.
3 shows the change in the capacity retention rate with the cycle of FIG. From Table 1,
It can be seen that the charge and discharge capacities are larger when lithium nickelate is mixed (Comparative Example 5) than when lithium manganate is used alone (Comparative Example 1).

When the content of lithium nickelate in the positive electrode increases, the battery capacity also increases. However, it is difficult to ensure safety. Therefore, the mixing amount of lithium nickelate is increased by weight with respect to the spinel-type lithium manganate. 1% or more by ratio 60
% Is desirable. The addition of Bi hydroxides and oxides reduces the battery capacity. However, if the amount of Bi is too small, the effect is not recognized. Therefore, the amount of Bi added is based on the total weight of the positive electrode active material. It is desirable to add in a range of 0.5% or more and 10% or less.

Table 2 shows Examples 1 and 2 and Comparative Example 1.
5 shows a comparison of the cycle characteristics of the discharge capacity at 45 ° C. of the cylindrical cells prepared in Nos. 1 to 5. Here, the initial capacity is 100
% Shows the capacity retention rate after 300 cycles.

[Table 2]

According to Table 2, it can be seen that the capacity was significantly reduced in Comparative Example 3, and the cycle behavior was clearly different from Comparative Examples 1 and 2. This is presumably because lithium manganate and lithium nickelate interact under this condition. On the other hand, in the batteries of Examples 1 and 2, it was found that the capacity retention ratio was significantly improved.

Further, when Bi carbonate, Pb, Sb and Sn carbonates, hydroxides and oxides were added, the cycle characteristics were also significantly improved as compared with Comparative Example 5. In addition, if the amounts of the carbonates, hydroxides, and oxides of Bi, Pb, Sb, and Sn are too small, no effect is observed, and if the amounts are too large, the battery capacity decreases.
0.5% or more and 10% by weight based on the total of the positive electrode active materials
It is desirable to add in the following range.

According to the present embodiment, a mixture of spinel-type lithium manganate and lithium nickelate is used as the positive electrode active material, and Bi, P
Since carbonates, hydroxides, and oxides of b, Sb, and Sn were added, it was possible to suppress the decomposition of the electrolytic solution or the adverse effect of the product thereof on the other active material. Cycle characteristics can be improved.

As described above, one embodiment of the secondary battery of the present invention has been described using a non-aqueous electrolyte secondary battery as an example.
The specific configuration is not limited to this embodiment,
Design changes and the like can be made without departing from the spirit of the present invention.

[0046]

As described above, according to the secondary battery of the present invention, in a secondary battery using a mixture of lithium manganate and lithium nickelate as a positive electrode active material, Bi, Pb , Sb, and Sn, it is possible to suppress the decomposition of the electrolytic solution or the adverse effect of the product on the other active material, and as a result, the cycle under a high temperature The characteristics can be improved. As described above, it is possible to provide a nonaqueous electrolyte secondary battery having a high capacity, excellent safety, and excellent high-temperature cycle characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing cycle characteristics at 45 ° C. of a cylindrical cell using a lithium manganate and lithium nickelate mixed positive electrode in each of an example of the present invention and a conventional example.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yuichi Kumeuchi 5-7-1 Shiba, Minato-ku, Tokyo F-term within NEC Corporation 5H029 AJ03 AJ05 AJ12 AK03 AL06 AL07 AL12 AM03 AM05 AM07 BJ02 BJ03 BJ04 DJ16 EJ03 EJ05 EJ12 HJ01 HJ02 5H050 AA05 AA07 AA08 BA17 CA01 CA08 CA09 CB07 CB08 CB12 DA02 DA09 EA01 EA12 EA24 HA01 HA02

Claims (5)

[Claims] 1. A secondary battery using a mixture of lithium manganate and lithium nickelate as a positive electrode active material, wherein the positive electrode contains at least one element selected from Bi, Pb, Sb, and Sn. Features a secondary battery. 2. The method according to claim 1, wherein the lithium manganate is Li _x Mn ₂ O.
₄ (where 1.02 ≦ x ≦ 1.25), and the lithium nickelate is LiNi _1-x M _x O ₂ (where M is at least one selected from Co, Mn, Fe, Al, and Sr) 2. The secondary battery according to claim 1, wherein 0 <x ≦ 0.5). 3. The weight ratio of the lithium manganate to the lithium nickelate is a: 100-a (4
The secondary battery according to claim 1, wherein 0 <a ≦ 99). 4. The secondary battery according to claim 1, wherein the element is added in a state of carbonate, hydroxide or oxide. 5. The carbonate, hydroxide or oxide,
The secondary battery according to claim 4, wherein the content of the secondary battery is 0.5% or more and 10% or less with respect to the mixture.